The present invention generally relates to the field of electronics. More specifically, an embodiment of the present invention provides self-biased driver amplifiers for high-speed signaling interfaces.
Chip-to-chip wireline communication consists of a chip sending and receiving data from another chip over wires incorporated on a board on which the communicating chips are placed. The sending chip drives the data onto the wire, otherwise known as a board trace, using a driver circuit. The receiving chip receives the data at the other end of the communication bus using a receiver circuit. In digital communication, the unit of data transferred maybe called a bit. In binary communication, where data is coded as a series of 1""s and 0""s, a 1 could be any voltage above a particular value, while a 0 could be any voltage below a certain value. The driving chip generally uses a driver amplifier to drive the board trace to the voltage level required to transmit the data. For example, in binary communication, the driver circuit charges the board trace to a high voltage to transit a 1 and to a low voltage to transmit a 0.
The performance of the signaling interface can be determined by the slew-rate and the voltage levels achieved by the driver amplifier. Slew-rate is the voltage rate of change as a function of time. Generally, a faster slew-rate and a higher voltage level result in a higher performance system, for example, by providing less jitter, more timing margin, and a faster data rate.
One determining factor in obtaining a fast slew-rate is the power supply of the driver. When the driver amplifier switches, the power supply collapses because of the inductance of the current path through the driver. Since the input of the driver amplifier is referenced to this power supply, a drop of the power supply reduces the gate-to-source voltage across the driver amplifier devices. The gate-to-source voltage determines the amount and rate of current the driver amplifier can source or sink to or from the board trace. Hence, a diminished overdrive voltage reduces the slew-rate of the voltage edge being transmitted into the board trace. Therefore, the drop of the power supply limits the performance of the driver amplifier.
The present invention includes novel methods and apparatus to efficiently provide self-biased driver amplifiers for high-speed signaling interfaces. In an embodiment of the present invention, a self-biased amplifier driver is disclosed. The driver includes a sensing circuit to sense a presence of noise in a power supply signal. The sensing circuit may include a current source to adjust an output signal of the sensing circuit in accordance with the power supply noise. The driver may further include: an amplifier coupled to the sensing circuit to amplify the sensing circuit output signal, a pre-driver to receive a data signal, and a driver coupled to the amplifier and the pre-driver to receive an amplifier output signal and a pre-driver output signal.
In another embodiment of the present invention, when the power supply noise is present the sensing circuit output signal may provide for a voltage change rate for a compensated signal that is faster than the voltage change rate for the data signal.
In a further embodiment of the present invention, a method of compensating for noise in a power supply signal is disclosed. The method includes: sensing noise in the power supply signal; determining whether the sensed noise meets a minimum threshold; if the noise meets the minimum threshold, generating a compensating signal; and generating a compensated data signal based on a received data signal and the compensating signal.
In yet a further embodiment of the present invention, the compensated data signal may have a relatively faster voltage change rate than the received data signal when the power supply noise is present.